HD66740 Datasheet, PDF (68/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
Partial-display-on Function
The HD66740 can program the liquid crystal display drive duty ratio setting (NL3-0 bits), liquid crystal
display drive bias value selection (BS2-0 bits), boost output level selection (BT1/0 bit) and contrast
adjustment (CT5-0 bits). For example, in the 10-line display mode (1/80 duty ratio), the HD66740 can
selectively drive only the center of the screen or only the top or bottom of the screen by combining these
register functions and the centering display (CN1–0 bit) function. This is called partial-display-on.
Lowering the liquid crystal display drive duty ratio as required saves the liquid crystal display drive
voltage, thus reducing internal current consumption. This is suitable for four-line display of a calendar
or time, or the display of only graphics icons (pictograms) at the top or bottom of the screen, which needs
to be continuous in the system standby state with minimal current consumption. Here, the non-
displayed lines are constantly driven by the unselected level voltage, thus turning off the LCD for the
lines.
In general, lowering the liquid crystal display drive duty ratio decreases the optimum liquid crystal
display drive voltage and liquid crystal display drive bias value. This reduces output multiplying
factors in the booster and greatly controls consumption current.
Table 26 Partial-display-on Function (10-line Display)
Item
Normal 10-line Display Partial-on Display (Limited 4-line Display)
LCD screen
10th line displayed
Only four lines on the
center of the screen
(from the 3rd to 6th lines)
Only four lines at the top
and bottom of the screen
(from the 1st to 3rd and
10th lines)
LCD drive position Not necessary
shift
(CN1–0 = 00)
Necessary
(CN1–0 = 01)
Necessary
(CN1–0 = 01)
LCD drive duty ratio 1/80 (NL3–0 = 1001)
1/32 (NL3–0 = 0011)
1/32 (NL3–0 = 0011)
LCD drive bias
value (optimum)
1/10 (BS2-0 = 000)
1/6 (BS2-0 = 101)
1/6 (BS2-0 = 101)
LCD drive voltage*
12 V to 15 V
(adjustable using CT5–0)
6 V to 8 V
(adjustable using
CT5–0)
6 V to 8 V
(adjustable using
CT5–0)
Boosting output
multiplying factor
Five times (BT1–0 = 10) Triple (BT1–0 = 00)
Triple (BT1–0 = 00)
Frame frequency
(fosc = 90 kHz)
70 Hz
88 Hz
88 Hz
Note: The LCD drive voltage depends on the LCD materials which are actually used. Since the LCD
drive voltage is high when the LCD drive duty ratio is high, a low duty ratio is suitable for low-power
consumption.
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